Technical Abstract:
Nearly 2 million Holstein lactation records from calvings during 1990 through 1997 (a 10% sample of Holstein data) that were acceptable for USDA genetic evaluations were used to determine age and genetic differences in predicted transmitting ability for milk (PTAM) and productive life (PTAPL) between surviving and culled cows. Only records from cows in herds that remained on test long enough to provide those cows with an opportunity to calve again were included. Cows sold for dairy purposes were excluded. Annual mean PTAM for surviving cows ranged from -145 kg for cows that calved in 1990 to 246 kg for cows that calved in 1997; corresponding mean PTAM for culls ranged from -234 to 170 kg. Annual mean PTAPL for surviving cows ranged from -.01 mo for cows that calved in 1990 to .74 mo for cows that calved in 1997; corresponding mean PTAPL for culls ranged from -.44 to .34 mo. Differences between survivors and culls ranged from 76 to 94 kg for PTAM and from .40 to .44 mo for PTAPL. Annual trends were 49 kg for PTAM and .09 mo for PTAPL for survivors versus 50 kg for PTAM and .10 mo for PTAPL for culls. Mean PTAM for grade cows across years (67 kg for survivors and -10 kg for culls) were higher than corresponding mean PTAM for registered cows (54 and -19 kg). Mean PTAPL for grade cows across years (.23 mo for survivors and -.18 mo for culls) were lower than corresponding mean PTAPL for registered cows (.69 and .32 mo). Mean age of cows that left the herd ranged from 65.2 mo for grade cows and 64.8 mo for registered cows during 1990 to 76.8 and 65.1 mo, respectively, during 1997. Trends were similar for surviving and cull cows, and surviving cows were genetically superior for yield and longevity. Age of cows that left the herd increased for grade herds over time.